Buttress thread is also known as breech lock form and refers to two types of thread properties. One type is a lead screw type; the other is a hydraulic sealing thread form.

• A. Two types of thread properties: one is a lead screw type, the other is a hydraulic sealing thread form.
• B. It is a taper pipe thread used for sealing.
• C. It is a standard square thread used for high-speed applications.
• D. It is used exclusively for optical assemblies.

Answer: (A)

Buttress threads are designed for two distinct applications, and the form is chosen based on how the thread is meant to carry load or seal. One variant is the lead screw type, where the thread profile is shaped to carry axial thrust efficiently in one direction. This makes it ideal for converting rotary motion into linear motion, as in power screws, where strong forward thrust is needed while backward movement is less critical.

The other variant is the hydraulic sealing thread form, where the geometry supports a reliable seal under pressure in hydraulic connections. The angled flank on one side of the buttress thread helps grip and seal as pressure increases, which is important for preventing leaks.

Seeing the statement that buttress thread refers to two types—one lead screw type and the other hydraulic sealing thread form—fits these practical uses. The other choices describe different thread categories or applications that don’t reflect the two-form concept of buttress threading.